Power sources typically convert a power or voltage input to a necessary or desirable power output tailored for a specific application. One such application is welding, for which power sources typically receive a high voltage (230/240V) alternating current (VAC) signal and provide a high current output welding signal. Around the world utility power sources (sinusoidal line voltages) may be 200/280V, 230/240V, 380/415V, 460/480V, 500V and 575V. These sources may be either single phase or three phase and either 50 or 60 Hz. Welding power sources receive such inputs and produce approximately 10-40 VDC high current welding output.
Often, a particular welding power source will be designed to operate in a market where utility power sources will be either 230 volts or 460 volts. Preferably, welding power sources for these markets are designed to be able to receive both of these input powers, and produce the desired output power.
While it is desirable that a welding power source be able to accept more than one input power, it is easier to design the welding power sources for a specific power input. For example, many power sources can not provide essentially the same output over various input voltages. Also, components that operate safely at a particular input power level are often damaged when operating at a higher or lower input power level. Moreover, operating an improperly linked power source could result in personal injury, power source failure or insufficient power.
Accordingly, many prior art power sources are designed such that input circuits are manually adjusted to accommodate a variety of inputs. The circuits may generally be adjusted by changing the transformer turns ratio, changing the impedance of particular circuits in the power source or arranging circuits in series or parallel. Generally, adapting to various inputs requires a power source to be opened so that cables may be adjusted to accommodate the particular voltage input--the operator manually links the power source for the input voltage. Usually, one connection must be linked for the power circuitry, and a second connection must be linked for the control circuitry. The two links were often located in different parts of the machine. Thus, re-linking for a different input voltage required that two separate links be made. Because of the physical separation of the two links it was possible that one link was properly made, the other was not properly made.
A power inverter which is capable of receiving two input voltage levels is disclosed in U.S. Pat. No. 3,815,009, issued to Burger on Jun. 4, 1974. The power invertor of that patent utilizes two switching circuits. The two switching circuits are connected serially when the higher input voltage is received, and in parallel to receive the lower input voltage. The switching circuits are coupled to each other by means of lead wires. The inverter is susceptible to operators errors in configuring the switching circuits for the appropriate voltage level, which can result in power surge, malfunction, and human injury.
Another prior art welding power source that requires manual re-linking is the Miller Synchron 300.TM.. The Synchron.TM. is designed to receive a variety of input voltages and frequencies. The user manually adjusts tie bars (copper bars) on a circuit board depending upon the input voltage. A window in the casing is provided so that the user can see the actual and desired locations of the bars for 230V and 460V input. Jumpers, located on a terminal strip away from the bars, also had to be adjusted. However, because this power supply had two independent links, it did not provide an easy way to insure that both links were properly made.
One disadvantage with manually linked machines is that the user had to remove the cover and/or decipher the jumper position to determine the power for which the power supply was linked. Accordingly, it was difficult for a user to readily determine for which input power the power supply was linked. Also, because the two links were independent, it was possible to make one correct and one incorrect link.
Other prior art power supplies automatically compensate for various input powers. An example of one such prior art design may be found in U.S. Pat. No. 5,319,533, entitled Power Selection and Protection Circuit Responsive to an Input Voltage for Providing Series or Parallel Connected Invertors. That design provides for connecting invertors in parallel for a higher input power and in series for a lesser input power. While automatically linked machines avoid the problem of mislinked machines, they tend to be more complex and more expensive.
Accordingly, it is desirable for a welding power supply to be designed to receive more than one input by re-linking the machine. Preferably, the machine should be re-linked with relative ease, and done such that it is difficult to make one correct and one incorrect link. Also, the user should be able to readily determine for which input power the machine is linked, without removing the cover. Finally, it is preferable that such a design would be relatively inexpensive and easy to implement.